1. Field of the Invention
The present invention relates to a locator for locating a conductive object. It is particularly, but not exclusively, concerned with a locator for locating an underground conductor such as a buried cable or pipe.
2. Summary of the Prior Art
The proliferation of networks of buried cables and pipes for many different utilities (electricity, gas, telecommunications, etc) has meant that any excavation of the ground is likely to be in the vicinity of a buried cable or pipe, and such excavation involves a risk of damage or interference to the buried cable or pipe, unless the location of that buried cable or pipe is precisely known.
In particular, the growth in the use of fibre-optic communication systems for telephones, cable television, etc has significantly increased the problems associated with excavation. Such fibre-optic communication systems have a much higher communication capacity than metallic conductors, but the costs consequent on damage or interference to the fibre-optic communication system are significant. Moreover, if damage occurs, it is more difficult to repair a fibre-optic connection than it is to repair a metallic connection. For this reason, owners and/or operators of fibre-optic communication systems normally require that, before any excavation can occur in the vicinity thereof, the location of the fibre-optic connection should be determined precisely, both by suitable location system and by visual inspection. In practice, this means that an initial excavation needs to be made to permit the official inspection of the cable, before any more extensive excavation can be carried out in the vicinity. Moreover, each preliminary location and excavation to enable the fibre-optic connection to be inspected must be repeated along the length of the fibre-optic connection, and this requires a significant amount of time and effort.
One type of conventional locator detects alternating fields from signal currents in a conductor, by means of a suitable antenna assembly incorporated in a hand-held receiver. Such an arrangement is applicable to fibre-optic connections because such connections normally have a metal sheath for protection purposes, and a signal can be applied to that metal sheath and detected.
In such conventional systems, a user carries the receiver and repeatedly makes measurements adjacent the target conductor until the receiver indicates that the conductor is present. Then, in order to obtain the visual inspection referred to previously, an excavation is made at the site determined by the locator, until the pipe, cable or fibre-optic connection is exposed.